1. Field of the Invention
The present invention generally relates to devices used to ventilate, cool, or warm persons, and more particularly to a blanket-type device which may be used to warm a body during surgical procedures.
2. Description of the Prior Art
Dozens of devices have been created to maintain a comfortable living environment for men and women. Air conditioning and heating systems for homes often meet this demand, but because of the expensive nature of such systems, and due to the fact that different individuals frequently have different desires concerning ambient conditions, several inventions have been devised to warm or cool smaller areas or spaces. A good example is an electrical heating pad, which may vary in size from about one square foot to the size of a bed, making it a heating blanket.
There have been several improvements on the idea of a heating/cooling blanket. One device, disclosed in U.S. Pat. No. 3,602,001 issued to Bauer et al., actually contemplates burning a fuel mixture within a garment. This patent is somewhat removed from more conventional devices, such as the one shown in U.S. Pat. No. 2,504,308 issued to L. Donkle. The Donkle device comprises a blanket having conduits therein which may act either as condensing coils or evaporation coils, depending on the orientation of a valve system with an external compressor. A similar product is depicted in U.S. Pat. No. 2,617,915 issued to G. Blair. Air is passed through a series of "tortuous" channels to provide even inflation. A unique variation of this idea is further shown in U.S. Pat. No. 2,991,627 issued to C. Suits, which discloses the use of Peltier junctions for cooling the person using the blanket. Another invention, described in U.S. Pat. No. 3,867.939 issued to Moore et al., is directed to a layered heating/cooling blanket having an absorbent stratum which may act as an absorbent bandage or be used to apply medicaments. Each of these blankets may be used in a hospital setting in which maintenance of proper body temperature may be critical.
The above-mentioned devices suffer one important drawback--the warm or cool air flowing through the blanket does not come into direct contact with the body, but rather heat transfer must be completed through the blanket material, dissipating the desired effect. This is especially detrimental in the case of small children whose total heat capacity is very low. Some other inventions, however, have overcome this problem by providing a series of air holes in the blanket itself by which the warm or cool air may be directed at the patient. One such invention is shown in U.S. Pat. No. 3,486,177 issued to I. Marshack. In that invention, a permeable cushion is placed over conduits having holes therein; the air flows upwards through the cushion and to the body of the person lying thereon. Obviously, however, the same problem of heat dissipation occurs in the cushion itself. Another version is depicted in U.S. Pat. No. 2,601,189 issued to N. Wales. That blanket utilizes a series of channels which provide uniform distribution of the air; however, the Wales blanket is designed to be placed over the subject, not underneath him, making it useless for surgical procedures since the surgeon must have access to the patient's body. If the Wales blanket is placed underneath the subject, the weight of the body will cut off distribution to the distal ends of the channels. A better design is disclosed in U.S. Pat. No. 2,512,559 issued to A. Williams, in which the two layers of material forming the blanket are spot welded or stitched, whereby the conditioned air may circulate around those portions of the blanket which are compressed due to the weight of the patient's body. Nevertheless, as a practical matter, it has been found that devices such as Williams are not suitable for their intended use because of the tremendous heat loss that occurs in the supplied air between the inlet hose and the distal end of the blanket. In other words, although the air exiting the holes near the inlet port is warm enough to provide heating capability, the temperature of the air exiting the holes which are farther away from the inlet port is close to ambient temperature, which typically has the undesirable effect of actually cooling the patient. If the temperature of the supplied air is raised in order to raise the temperature of the air exiting the distal holes, then the air exiting the proximate holes is so hot as to cause discomfort, and even first degree burns. It would, therefore, be desirable and advantageous to devise a blanket which could warm the body of a patient from underneath, which would overcome the above-identified drawbacks.